There is increasing interest in energy and transport technologies based around hydrogen. It must be emphasised that hydrogen cannot replace oil as a source of energy - there are no significant reserves of natural hydrogen. Instead, other energy sources are used to make hydrogen, which then becomes a transportable store of energy.
Hydrogen Fuel Cells
Fuel Cell Vehicles
In a vehicle the electricity produced by the cell is used to power an electric motor, lights and so on. Some advantages of using a fuel cell are:
· The only emission from a working cell is water, so they have the potential to improve air quality in congested cities
· Fuel cells and electric motors are much quieter than engines
· Unlike electric vehicles using batteries, which need lengthy recharging, refuelling is quick
Fuel cell cars are not in general production, but trials of fuel cell buses are in progress in nine European cities, including London (route 25).
Electrolysis and reforming both require a considerable amount of energy, and the hydrogen generated is therefore acting as an energy store. The electrical energy eventually produced by the fuel cell cannot, of course, be more than the energy needed to make the hydrogen in the first place! A hydrogen fuel cell is not necessarily a source of "clean electricity" - it really depends on how you produce the hydrogen.
In order to use hydrogen in a fuel cell vehicle, a sufficient quantity has to be stored in a safe, easily transportable form. There are currently several different approaches.
Alkali Metal Hydrides
Another way of producing hydrogen is using reactive metals and water. Sodium hydride (rather than sodium metal) is encapsulated inside polythene spheres, about the size of a table tennis ball, referred to as powerballs.
The power balls are stored in water inside a hydrogen generator, and are cut in half automatically as required to release the sodium hydride and produce hydrogen. During refuelling sodium hydroxide, also produced by the reaction, is removed along with empty cut spheres, and fresh power balls are put in.
The sodium hydroxide can be used to make more sodium hydride, and the plastic shells are recycled into new powerballs.